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Oct. 8, 1929. CLEMENT 1,730,407

FREQUENCY CONTROL FOR RADIO DISTRIBUTING SYSTEMS Filed Feb. 9, 1924 5 Sheets-Sheet 1 Oct. 8, 1929. E. E. CLEMENT FREQUENCY CONTROL FOR RADIO DISTRIBUTING SYSTEMS Filed Feb. 9, 1924 3 Sheets-Sheet Ill FREQUENCY CONTROL FOR RADIO DISTRIBUTING SYSTEMS Filed Feb. 9, 1924 3 Sheets-Sheet 3 JO FI 10 wax/asses 7:4 EPl/arlg gnvento'c Patented Get. 8, 1929 UNITED STATES PATENT OFFICE' EDWARD E. CLEMENT, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO ED- WARD F. COLLADAY, OF WASHINGTON, DISTRICT OF COLUMBIA FREQUENCY CONTROL FOR RADIO DISTRIBUTING SYSTEMS Application filed February 9, 1924. Serial No. 691,822.

My'invention relates to radio broadcasting systems, andespecially to those designed for regional distribution. It has for its object to produce a system which shall meet the following requirements:

1. All receiving instruments in the system to be standard and fixed in their tuning, so as to operate always on one and the same wave length.

2. All receiving instruments to beablc to receive efficiently, with either telephone headset or loud speaker, all modulations and nals transmitted from all sending stations, regardless of the wave lengths on which they are transmitted.

3. All receiving instruments to be of very simple character, and so connected to the wired circuits with which they are identified,

that they may be supervised, tested, supplied with electric current, and if desired, their service metered, from a central said wired circuits.

4. All receiving instruments to be available for ordinary telephonic use over the wired circuits, as well'as fulfilling the function of radio telephone instruments, that each radio receiving instrument may be also an extension telephone, if so desired.

5. All reccivin' instruments to be so designed that'thev may be grouped or connected either as many-party-line subscribers on the wired circuits, oreach station may have a private wire, all in accordance with stand ard telephone practice. This also implies the sending and receiving of signals to and from party line stations, and the individual metering of several parties on one line.

6. The entire system of radio distribution, with all the instruments thereon, to be operable independentlv of the telephone exchange system, with which it is associated, and whose wired circuits are used in the radio distributing system. This implies further that the two systems may be separated in management, as for example, in time of war or public necessity.

7. All instruments and their circuits to be so related to a central radio exchange and its operating switchboards, that direct communication may be had both ways, during point, over rents from the central ofiice to the subscrib' ers, and by audio frequencycurrents from the subscribers to the central ofiice. This implies not only that a subscriber can speak to the central office operator at any time, but also that performers may hear the applause of the listening subscribers.

Other purposes and features. of the invention will sufficiently appear from the detailed description hereinafter. Briefly stated, I attain my object and meet the foregoing requirements as follows:

(-1) and (2) are met by providing a central office receivingset, to receive modulated waves from distant stations, which I may call primary stations, on various Wave lengths, and while faithfully reproducing or relaying the modulations, transforming the frequency of the carrier waves and transmitting a resultant modulated long wave over the subscribers lines to the radio telephonesubstations. The long carrier wave used for this final wire line distribution is always the same. regardless of variations in wave lengths of received signals. This means that-the central office receiving and relaying apparatus must be not only in effect a frequency transformer, but must also be an adjustable or variable frequency transformer, adapted to take in variable frequency through a wide range on its input side, and to produce always the same wave length on its outputside, maintaining the same modulations without loss. 'In certain prior copending applicatimes I have describedone means for doing this which involves however a reduction to audio frequency. In the present case I prefer to use the heterodyneprinciple, which also enables me to provide a local balancing circuit containing an oscillator and if desired a modulator stage, to maintain continuity of service with the same apparatus for local programs when distant stations are not sending or when it is not desired to receive them. Such a receiving and relaying apparatus, therefore includes as elements a tunable receiving circuit for distant stations including an antenna or its equivalent; (b) a local oscillator circuit tunable for heterodyning the carrier waves received from the distant stations; (0) a second local ((1) intermediate frequency filtering and.

amplifying means tuned to the constant wave length of the desired beat waves which are to b" transmitted as carrier current to the subscribers stations;.(e) modulating means for either orboth of the local oscillator'circuits employed in heterodyning; and (f) means for tuning or adjusting the subs'cribers circuits permanently to the fixed wave length to be distributed thereover. For examples, the distantstation receiving circuit maybe adapted to wave lengths from say 150 to 500 meters; the first local oscillator circuits must then have the same range of frequencies, the first oscillator circuit being tuned in receiving to give a constant difference of say 30,000 cycles per second from the carrier frequency of the distant station being received; and the second oscillator circuit being tunable within the said range to the same frequency or wave length as the last distant station received. The resultant or beat frequency due to any combination thus set up is constant, so that carrier current at a standard wave length of'say 10.000 meters is always impressed upon subscribers lines. Moreover, the intermediate frequency amplilying means is permanently tuned to the wave or beat frequency, which for reasons Well understood in the art can be ampli'fied more efliciently than short waves. By providing modulating means for the first oscillating circuit, local modulations can be impressed on the-beat wave or carrier current transmitted to the subscribers, in, addition to the modulations of the carrier waves received from a distant'station. Thus, local announcers may interpolate features or remarks in a program, or local performers or instruments may cooperate with the ,per-

formers at the distant station. The arrangement is sufiiciently elastic so that a number of performers at different points both within and without the local'area, may be associated together, as for example different sections of an orchestra ordiffercnt orchestras or bands, or different parts of a chorus. To enable the operator at the local central station, and the local perfor-mers if necessary, to listen in on the waves as received and as heterodyned, Iprovide'one or more localreceiving circuits preferably connected on theoutput side of, the radio frequency amplifying element in the above combina- .tion. This is necessaryin any case for the 'local operator, in order that he may properly tune his circuits. His instrument connected as stated. would be permanently tuned to the long beat, that is to say. 10,000 meters wave length; and hence would serve as a wave meter for theexact adjustment of his local as a further check. scribers instruments; so that the actual perwhich are standardized for the fixed wave length of the beat, assumed in this case to be 10,000 meters. As set forth in prioricopending applications, and as stated above at (3) the operator has access over subscribers lines to the subscribers receiving instruments, for the purpose of supervising, testing, etc. The operator can therefore check his own receiving circuit, and calibrate the entire system so to speak, by first adjusting his oscillator circuits so that his own receivingset is at maximum efficiency, and then listening in on various subscribers. circuits This access to the sul formance of the receiving elements in the systen'i may be ascertained from central, I consider very important, as it eliminates all elements of uncertainty and gives the central station exact knowledge and perfect control without disturbil'ig the subscribers and without any necessity for sending out inspectors or maintaining test stations.

(4) and (5). I employat the subscribers station as the essential elements a coupler, a rectifier or detector, a telephone receiver,.and a telephone transmitter. A telephone condenser of the usual radio type, a tuning condenser if desired, and separate switches for thc'high frequency receiver and t'het'elephone transmitter may also be employed, as well as a step down transformer so that a. low wound telephone receiver may be used, making the instrument for audio purposes an ordinary telephone. If used" on a party-line, as an extension phone, it may be desirable also to provide the usual ringer, and if head telephone receivers are to be employed, a crystal detector or the equivalent may be used. lVhere a loud speaker is desired, a single stage of audio amplification is ordinarily sufiicient, and if a dynamic-type of loud .speaker is employed, current can be taken over the telephone line so that either with or subscribers station can be eliminated. Extreme sensitiveness is not necessary, because while the modulations are the same'modulations originally impressed on the short carrier waves sent from the distant stat-ion, they are carried to the subscribers on a low frequency carrier current, that is to say, on a long wave length, over the wires, and with substantial reinforced energy impartedto them atthe local distributing station. With respect to the party-line feature, it goes without saying that when the high frequency receiving instrument is designed with the necessary elements to make it an extension telephone set. it can be adapted to any use for which an ordinary telephone set is usually employed,includiri party-line service. The transmission of modulated carrier currents over a party-line at one or more frequencies and in sutiieient volume to supply a plurality of stations thereon offers no difficulties, inasmuch'as the lines to the subscribers stations are in effect extensions of the bus bars or wires at the central station, which must be supplied with sutlicient carrier current for all the lines connectedto said bus bars. Arrangements for this purpose, such as amplifier tubes in pa allel. are available in the art, and need not be specifically described.

(6) and (7). As will hereinafter appear, the radio exchange is operated in this system as an entirely separate entity from the telephone exchange to which the subscril'iers lines may be connected. It is true that the provision of a separate radio switchboard and opcrators station would probably be sutticient in conjunction with a telephone exchange switchboard, for the important objects herein set forth, but as this present system is only part of a complete organization which may be country-wide, and in many dis tricts involve groups of exchange centers, I have chosen to treat the radio telephone system, not as an auxiliary to the telephone system, but as a system complete in itself, of equal importance with the telephone system, but having very different functions. The purpose of the telephone exchange system is to enable individual subscribers to communicate with each other. It afi'ords no means of simultaneous communication with all of its subscribers. or from all of its subscribers to any given point, or of simultaneous communication with any lnoresubscribers than can be reached at one time through the percentage of connecting devices provided on the telephone switchboards. The radio exchange systen'l, on the other hand, is not adapted nor intendedto interconnect individual subscribers, but is preferably adapted to handling subscribers in masses or groups, from which individuals may be selected by voluntary action. With the apparatus hereiubetore mentioned at a subscribers station, he may be called individually and communicated with in the ordinary way over his telephone circuit. by the radio operator. or he may be called by name during the broadcasting, and may respond over his telephone circuit. using his radio instrument as a telephone for the purpose, or he may be called either by wire or my name, and connected to the broadcasting circuit at central so that he in turn may communicate by broadcast with all the other subscribers. Various other combinations can be made. sufficient to make the radio exchange system as such very valuable as a separate means of communication in time of war or public emergency.

My invention is illustrated in the acconr pauying drawings in which:

Fig. 1 is a diagram of receiving and transwith modulator adapted to connect to the coupler in Fig. 1.

Fig. -l is a diagram showing a subscriber's rcceiv ing instrument provided with a telephone transmitter. and connections such an extension telephone.

Fig. 5 is a similar diagram showing a further modilication of the subscribers station circuits in which a crystal detector is employed for simplicity, in parallel with the high frequencytelepllone IQtQiVt r.

Fig. 6 is a further diagram of another modi tication employing the same elements as Fig. 5, but with the crystal detector in series with the telephone receiver, and the latter shunted by a by-pass condenser.

Fig. 7 is a diagram of a still further moditication in which a vacuum tube detector is employed, with its filament supplied with energizing current over the telephone line from central, and its plate circuit connected across the subscribers telephone branch, which may be supplied with a special form of telephone receiver, or with the ordinary telephone set, upon which the subscriber may then receive all messages, both telephonic and radio.

Fig. 8 is a diagram showing a tuned coupler spanning the gap between the radio exchange terminals and the telephone exchange terminals of a line.

Referring to the drawings, R indicates in general a radio central ofiice or exchange through which modulated waves received from a distance are relayed, and from which local originating signals and programs may be transmitted to subscribers in a local area or region immediately surrounding said central otlice. Transmission to the subscribers station is illustrated in Fig. 2 as by means of wired circuits over which modulated waves from central are guided. These circuits'af ford access to the receiving radio telephone stations by central office operators and wire chief for testing purposes, and for supervision and control. They also serve to carry energizing current, as for example battery current or low frequency alternating current, to the subscribefis station for use in connection with vacuum tubes and loud speakers. if the same are employed. A third service which may also be imposed upon the wires is that of metering the use of the radio receiving sta tions in substantial accordance with telephone txchange practice. It is not the purpose of the present application to develop detailed connections and characteristics of the line YOU I circuits or the si1bsclibers.receiving apparatus; but rather to set forth'the combinations of central ofiice and subscribers apparatus necessary to' realize the objects hereinbefore stated. The first of these is to produce fre quency transformation at the central station, so that any distant station may be received as at present, on its own wave length and the modulations thereof may be preserved but transmitted at a ditferent wave length to the local subscribers, said wave length being that to which their iustrumeutsare standardized and permanently tuned. This arrangement lends itself with particular readiness to wired circuits, or line radio transn'iissiou to the sub Scribers, because if incoming waves are transformed in freqnqicy to much longer waves, as

forexamplo, waves of 10,000 meters in length,

not only are those long waves more suitable for transn'iission over the subscribers wired circuits, but they are also susceptible of amplification at the central station and if desired at. the subscribers stations, with higher etiiciency than shorter waves. The frequency suggested, viz; 30,000 cycles per second, approaches audio frequency so nearly, that transformers may be employed with iron cores, thereby rendering it possible to employ said transformers through a range of frequencies extcuding'into the audio.

lVhile in copending applications I have described other means of changing the frequency of the carrier wave in relaying from distant stations to subscribers, in the present case I show for this purpose av superheterodyne circuit, employing two local oscillator circuits,

eithcr or both of which may be equipped with modulators. In Figs. 1 and 3 both of said oscillator circuits. are shown thus equipped. In Fig. 1, 1 is the station antenna, 2 is the coupler, and 3 is the ground connection, all of usual or any desired construction suitable for the purpose. For a purpose presently to be explained, I include switch contacts 4 and 5 in the antenna and ground connections and another switch contact 6 which when closed, shunts a load coil in the local receiving circuit. The coupler 2 in the present case has three windings, 2, 2", and 2 The first of these is the antenna coill The second is the secondary'coil in the receiving circuit, and the third. 2, is a coupler for the oscillator circuit of Fig. From the coil 2 wires 7 and 8 extend respectively to the grid and filament terminals of the first tube 9, which is a detector tube. It may he stated here that the specific circuit I have chosen for illustration employs two detector tubes, one for heterodyning, and the second at the subscribers station. The wire connection 7 to the grid 9, has interposed init the usual grid condenser 10 and grid leak 11. The wire 12 from the plate 9" extends to the primary winding of a radio frequency coupler 13, both windings of which are shunted by by-pass condensers of suitable capacity. The return from the opposite end of the primary'winding of such coupler 13 is by way of wires 14, 15 and 16 to the filament 9. Across the wires 7 and 8 a tuning condenser 17 is connected, and the leads 1819 from the secondary winding of the coupler 13 pass to the first tube 20 of the radio frequency amplifying tubes 20-21 and 22, constituting the usual three stage radio amplifying unit, with coupling trans formers 23 and 24 between the tubes. On the output side of this amplifying unit wires 25 and 26 are connected to one winding of a. coupler or transformer 27, the other winding of which is connected through suitable condensers to subscribers line wires, or to the bus bars on which said line wires are grouped according to their classification and method of feed.

The foregoing represents a method of receiving and amplifying modulated waves and putting the same on subscribers line wires, as generally set forth in my prior copending applications Serial No. 597,422, filed October 27, 1922, Patent No. 1,576,308, granted March 9, 1926, and Serial No. 681,992. filed December 21, 1923, the principal difference up to this point being the use of the detector tube 9. In order to transform the wave length of the carrier current amplified and transmitted over the subscribers lines I employ a local oscillator circuit designated as a whole by ()0. This may be of any desired and suit able construction and arrangement, with or without modulation, but is shown as of a known type with modulation according to the Heising method. The choke coil in the battery circuit required by the I-Ieising meth od is shown at 28 in the upper right hand is connected to the outer terminal 30 of the coil31 and the grid and on the other end is connected to a switch arm 37 which may be shifted to one or the other of the points SW' and LIV, the former being connected by wire 38 to the outer side of the coil 3 and also through the condenser 33 and coil 30 to the plate; while the point LIV is connected direct through wire 39 to the circuit of the plate of the oscillator 29. IVhen the switch is on the point S'W therefore the condenser 34 is across the terminals of the coil 31 and when the switch is on the point LIV it is across the plate and grid terminals. The modulator circuit MC includes a tube 40 and a modulating transmitter and transformer 41 and 42 connected circuit MC when desired the switch con tacts and tti are provided in the wires 43 and 44.

'ith the oscillator circuit ()C incoming waves in the antenna circuit l-2 3 may be heterodyned through the tube 9 so that the modulated carrier wave at heat tre uency. which for present purposes has been assumed as a constant at 30,000 cycles per second, will be propagated through the coupler 13 into the amplitier circuits. and after amplitication by the tubes Qt) 21--22 will be imposed upon the suhscrihers lines typilied at )(l fll in Fig. 1 or the bus wire 30. 51" leading t the busses 5Q53, from which tfilllltttlOl Htfll he made to any subscriber's line so ar a shown in Fig. Q. The connecting means between the husses and the suh crihers' lines are shown as jacks and plugs 5% $3 36. but it is to he understood that 1 do not limit myself in this respect and that this connection maybe by any desired m an including a gap spanned by the amplili d ra-lio warm, as indicated in Fig. 8 ot' the drawings. the use of such a tuned gap (loin; away with the necessity for physical connection het ween the radio exchange, terminals and the telephone exchange terminals of the lines.

Referring to Fig. 8. l have therein shown the has wires and 51 connected to a loop 5?. taking the place of the terminal jack 54 in Fig. 2. An exten ion loop 5.? may then he connected to each of th line extensions. DU -MW correspoinling to the line extensions 50 and 50 in Fig. The loops Trt iitr are shown as tuned hy means ot condensers as usual. The snh criher s receiver Pm and his telephone Sf may he the same as in Fig. i. In practice. there will also he m ans indi cated by switch contaas as ST and 5% to hreah or interchange the connectio het ween any particular hetcro lyning' set such a shown in Fig. 1. and any parti ular group of lines or tle hus therct'or as typilied in Fig. 2. Further rct' ren will he made to this hereinat'tcr.

llel'erring to Fi Z llir1\eth-.-rein hown a s cond o illat: circuit ()t" containing the sam elementa the tir t oscilla or Ht. but without the sh rt and long wave .'it- 'h 3T whicl however may h upplied it the second o cillator is to cover the sam !"1llf'ft of t'reqncm-ies a the l rst oe illator. This second o-cillator is connect d to the nriiu r ceiving circuit hv wire iiis c tend ng to a coupler coil 2* inductively r lated to the primac and eeon-lary t' the main coupl r 2. Thi connection may he otlwrwise ar ranged. s long tl: the tunetion t the econd oscillator is preserved, which is to replace the distant source of waves forming one component which by composition with the other component due to the oscillator OC produccs the heat waves herein-before described. \Yhen any distant station has ceased transmitting. or when it is desired to substitute local matter l'or a part of the distant program. the operator opens the antenna switches -'l5 and closes the switches 5'5 in the leads 4T- is to the halancing oscillator 00', which obviously should he previously tuned in any desired or well known manner to the same frequency as the distant station which it replaces.

Referring to F-ig. Q. the wires 50 and 51 are connected to the output side of the heterodyne circuits in Fig. 1. and supplythe hus wires 52-5L to which they are connected, as hy jacks and plugs. subscrihers line wires typilicd hy 50 and 51*, leading to a subscriher's station SS. At this station St indicati's the suhscrihei"s telephone and S7 the subscriber's radiophonc receiver. The telephone shown is of the \Vcstern Electric standard common battery type; and the radiotetephone includes a telephone receiver .37. shown as a head set. a crystal detector 5*. a conden er 3. and a switch (30, which may he operated by a receiver hook lever (30". This set is connected hy a coupler (31 to the wires 50 and M with an interposed tuning condenser (3'3 and cut-ofl' switch contacts (53 and 64. by means of which it may be disconnected from line at will. By making these switches in the torm of a double pole douhle throw unit. the receiving set may conveniently be connected toan antenna and ground when cut ott t rom the line. This connection may also he. effected by the telephone switch hook 6.3 in the telephone set Sf. after the manner of hook Gt)"; so that it desired the radiotelephone set may be operated independently when the telephone is in use for conversation over the line.

l have shown line extensions 50 and :"ull extending to a pair o t' iacks 5G and no, rep resenting multiple terminals of the telephone line on the telephone switehhoard at the tele phone central exchange. It is to be understo d that all de irable and necessary hattery supple connections. relays. signals. and assoiatwl devices are implied without specifi ilwtrat ion.

The left hand side of Fig. 2 is supposed to represent a part of the radio telephone central exchange containing the apparatus of Fig. l. The out ide lines to the suhscrihers' stations are supposed to he included hetw en the dotted lines tl l and (37. and the right hand s de only. .\t the station ll. the tll llltll'tltllh of Fie. l may be duplicated as indicated at GR and (ill in Fig. :2. supplying hus wires 52---55l, 52 -53 etc. The e duplicate. hetto showihe sub riber's station SSJ ing the standard wave length.

erodyning sets meet several reipiirements. laeh may he tuned to reeeive tr at a distant. station, or to send out its own wav s, on a wave length diilerent from the others, pro vided the heterodyne eireuit is adjusted so as to deliver to the suhserihers eurrems hav- Again. they lnay be tuned in pairs so that when one apparatus is relaying t'rom a distant station. the second one is ready to t'eplaee it. with its. oscillator eireuit ()C (Fig. 3) tuned to or respond to the di tant station which it will replaee. Again. for preventing reeeption of the signals hy those who are not suhserihers. the latter may he grouped on the hus wires 52"-5 eta, and the suhserihers may also he ('l;l. -lllt(l according to the program they wish to reeeive. lat-h of the ap aratu es typilied in Fig. l and at (3% and (it) in Fig. '2 may delive' a ditl'erent program. and it' the demaml exists there may he a sin'iieient nun;- her of these relay sets to enahle the suhserihers to receive at. will from any ol the prineipal hroadeasting stations. The seleetive intereonneetion of the lines with the husses 5Q53, etc,., as indieated in Fig. 2 hy plugs and jtlth'Fl may he either automatic or manual, and may he variahle or fixed for a time.

The suhserihers eireuits typified as 91' in Fig. 2 may he varied in various ways and in particular by including a telephone trans mitter and otherw se arranging the connections so as to make the set in effect an extension telephone. indieated in Fig. 4. In this figure the line wires Sti -51 ar conneeted to one side of a coupling eoil 61 through a tuning eondenser and in parallel therewith through the wires 51 to the suhserihews ordinary telephone as shown in Fig. 53. The other or loeal side of the line coupler (it goes to a high l'requency receiving set symboliz d hy the reetangle RS. the output terminals of this set hein; (.Otllltt'lttl through a trand'ormer G1" to the loud speaker 5?. The usual filament and plate hatteries and it are shown. the former eon trolled hy a hlade s ot' a switch S. seeond .hlade s controls the connection of the induetion coil I whieh when eonneeted fo ms with the transmitter T and the loud speaker 57 a standard e tern Elertrie extension telehhone set. Thi set may le u ed eoii'ieidentally with receiving high trequenov waves over the line on a set 115'. a teparate teleph ne ree iwr heing provided. it desired. The cirruit of this exten ion phone is the same as the eireuit shown at suhsr'riher tele phone station 1 in Fig. 2. The transformer H1 or its erpiivalent in other eireuits sueh as Fig. T. may he a step-down transtormer so that the output will he at ordinary telephone voltage. and an ordinary low wound (rommereial telephone rereiver may he employed. In such case an ordinary suhserihefs telephone may he used for receiving as indi at'ed in Fig. 7. would employ one or more vaeunm tuhes. and the telephone receiver, energized through a step down transt'ormsr would art as a loud speaker.

Figs. 5, (t, and 7 show other possihle vari ations of the suhseriliens eircuit. In all of these forms I have shown the eonpler (31 or 61 with an iron eore. liceause th frequeney is just above the limit. ot' audihility. and these transformers ean there fore he used for repeating hack audio l'requeneies into the telephone line from the suhscrih ns re eiving set HS circuit. In Fig. T a tuhe detector is shown whieh takes its hattery supply for hoth plate and filament from the telephon line. and in this case the plate cireuit would repeat into said line. heside etleeting regeneration through the eoupler (il. l have indirated a teleph ne head set hridged a ross the wires 5t) and 51: and it is to he understood that underlying the design in all of these ligltres is the idea of the eent 'al otlice operator listening in to the actual reception at the suhseriher's station.

I claim:

1. In a radio telephone system of hroadeast distrihution. a eentral station and a plurality of suhserihers stations intereonneeted by individual line wires. :1 source of modulated high frequency radio waves at the eentral station. an oscillator also at the een tral station tuned with relation to said high treqreney modulated waves so as to produce a relatively low frequency heat wave. ahove the limit ot: audition. means to transmit said heat waves earrying the original modulations. over individual line wires to the suhscrihers stations. and means. at. eat-h sulrserihefis station controlled ertilely hy the suhseriher tor deteeting said waves and rendering the modulations thereon audihle to the suhsrriher.

2. In a radio telephone system of broadeast distrihutiou. a central station and a plurality of suhsa'ihers stations. with individual line wires intereonneeting them. means at the eentral station for reeeiving modulated high frequent-y waves. means al o at the eentral station tor generating high trequenPy waves adapted when coinliined with the lirst mentioned waves to produee a relatively low frequency heat carnving the original modulations. means tor eomniunicating' said modulated heal frequency interchangeal ly to the suhserihers' individual lines. and means in. each line for detecting the same and rendering the modulations audihle to the suhscriher.

3. In a radio telepln'me system of broadcast distrihution. a central station and a plurality of suhserihers stations with individual line. wires intereonneeting them. a eommon heterodyne receiving and transmitting apparatus at the central station having input v v- & 'lhe reeeivin' set lit in this ease lit) tit

terminals adapted to reeei ve modulated waves from distant stations and output terminals adapted to deliver the modulated heat wav due to heterodyning said input waves. means for eonneeting said output terminals interehangeahle or in eommon to the suhserihers individual lines. and individuat means at the suhserihers' stations 't'or detea-ting the heterodyned waves and rendering the modulations thereon audihle to the suhseriher.

-l. In a radio telephone system of hroadeast distrihution, a eentral station and a plurality ot' suhserihers' stations and tuned line wired eirruits intereonneeting them. means at the eentral station for heterodymug into the sunserihers' lines so as to transf rm modulated high t'rei ueney waves ol" varying and indeterminate ll'tttlttlltlts into modulated low 't rtapieoey or long waves of standard or ti:-:ed t'rer ueney therein. and means at the Slit)- s 'rilzers station for dettnting and ieetit'yiug said low t'reoueney waves and rendering the modulations thereon audihle to the uh serihei'.

7. In a radio telephone system of tn'oa l east distrihution. a eentral station and a php ratity ot suhserihersstaiiom. a plurality of lines intereonneeting them. suhsrri ier. \e eeiving apparatus and lines tuned to a wow stant t're ueney. means at the eeatral station to heterodyne modulated high t'reznaeney waves ot varyin; frequent-y and propagat the resultant heat waves at a eonstrznt tie queney into the suliserihers' lines so to pin duee therein relatively modulated waves, ot the lived fl'ttlll(lt( to whit-h the lines and sul serihers' stations are tuned.

(3. In a radio telephone system o" hroadeast distrihution. a rentral station and a plu ratity ot snhserihers' stations and line wires intereonneeting them. reeeiving apparatus at the suhserihers stations tuned with the lines tor et'tieient reeeption at a eonstant trequeney. means for heterodyning high hequeney modulated waves of varying treo ueni-y to, produee eorresporulingly modu lated heat waves of said eonstantl t'retpieney in the srhserihers lines. and means to varv the t're uenry ot'one ot'tlie heterodyning high t reipieuey waves to maintain the heat eonstant in the snli erihee lines.

7. In a system of radio liroadeast distrihu tien. a r iitral station and suhserihers stations with snhseriher lines eonneeting the suhs rihers' stations with the eentral station. a radio reeeiving apparatus at the eentral station having its input eireuit tunahle to reeeive at various 'treuueneies. a loeal osrillator a eiated with said reeeiving set. tunahle to produre waves at a suitahle t'reipieney to heter dyne with the ineoming waves in said input eireuit, a seeond loeal oseillator also tts-(leiated with said reeeiving set and tunahle to furnish the input eireuit thereof with waveof various frequencies through the same range as those of the waves reeeived from external sourees,a tuned eireuit adapted to. reeeive the heat waves due to said heterodyning, whether between the first loeal oscillator and the distant station, or between the two local oseillators. amplifying means connecting said tuned eireuits with a suhserihers line and means to impress modulations upon the waves supplied to the input eireuit hy one of said oseillators.

7 8.. The system deserihed in claim 7, having means to impress modulations on the waves in either loral oseillator circuit at will.

5). The system deserihed in claim 7 having means to impress modulations on the waves in both of the loeal oscillator eireuits simul taneously.

It). The system deserihed in claim 7, with means simultaneously eontrollahle. to coinhine modulated waves reeeived on theinput eireuit from the external source. and modulated waves reeeived from a loeal oseillatt'n', so as to produ e in the tuned intermediate fre quen y eireuit. a single h at, wave Carrier having hoth sets of modulations impressed thereon.

ll. In a system of radio hroadeas dist rihution having a heterodyne reeeiving set, without a seeond detertor or audio amplifier means for supplying modulated waves from exterml sonrees to the input eireuit of said.

heterodyne reeeiving set, means [or separatel supplying modulated \aves at suitahle heterodyning trequeney to said input eireuit, a eommon tuned output eireuit theret'or adapted to reeeive and transmit a single snpet-audio wave train of heat t'retpieney earryiug all the initial modulations, m ans eonnet-ted with said eireuiti for amplifying said mmlulated earrier wave, at said heat l're queney and output terminals for said amplil'ying means. together with distriluitive wire eireuits tuned to said heat l'requeney wherehy the modulated and amplitied single wave train may he transmitted to the ultimate reeeiving stations.

12. A re eiving and relaying apparatus 't'or systems of radio hroadeast distrihution. ineluding as elements a tunahle reeeiving ei' euit t'or outside stations sueh as an antenna or its equivalent. a loeal os illator eireuit tunahle t'or heterodyning with the earrier wav s reeeived from the said outside f-itltlt ll r stations to produee a resultant heat. wave: and a seeond leeal oseillat r rireuit tunahle t re plat-e the earrier wave t'requeneies ot' the external or distant: station.

t l. i\ system ot radio hroadea t distr hir ti in ineluding the apparat is deserihi-d in etaiin 12 with the additi nal elements of sul seriher reeeiving eireuits permanently tun d to th fixed wave length to he distrihuttal thereto-er. and means for maintaining the said intern'iediat trequeney or heat wave produeed hy heterodyning.

14. A system of radio broadcast distribu tion including the elements described in claim 12, and in addition thereto. intermediate frequency filtering and ampli tying meanstuned to the constant wave length of the desired beat waves which areto be transmitted as modulatcd carriers from the relaying apparatus.

15. A system of radio broadcast distribution including elements described in claim 12 and in addition thereto the following: a plurality of subscribers stations adapted to receive modulated waves distributed from said common receiving and relaying apparatus, means For tuning or adjusting the subscribers circuits permanently to a fixed wave length, an intermediate frequency filter and amplifying means in said relay apparatus, whereby the output of the same will be maintained in constant. tune at the fixed wave length to which the subscribers receivers are adjusted.

1G. The receiving and relaying apparatus described in claim 12 with the addition of modulating means for one of the local oscillator circuits employed in heterodyning to affect modulation of the resultant heat wave.

17. In a system of radio broadcast distribution, the apparatus described in claim 12 arranged so as to produce an intermediate frequency or beat wave, a circuit for said long or intermediate wave permanently tuned to the frequency thereof and subscribers circuits connected to said tuned circuit together with means at the subscribers station for demodulating the waves received.

18. In a system of radio broadcast distributioma central station and subscribers stations, a receiving and relaying apparatus at said central station adapted to receive at divers frequencies from distant stations. and to transmit to the subscribers in its local area at a fixed standard wave frequency, an operators demodulating and sound reproducing device adapted to be connected to the output circuit of said relaying apparatus, and means whereby the operator may listen in on the subscribers circuits. whereby said operator can first check his own receiving circuit and calibrate the entire system by adjusting his oscillator circuits so that his own receiving set; operates at maximum efficiency. and then further check the correctness of the tuning by listening in on one or more subscribers circuits.

19. In a system of radio broadca t distribution. a central station equipped with radio receiving means having an output circuit terminating in a common radiator, a plurality of subscribers wired circuits extending from said central station to subscribers stations. and a tuned receiving antenna at the central station for each of said sul.)scrib ers lines, wherebymodulated high frequency wave trains may be distributed over the subscribers lines bv radiation without physical connection therewith at the central station. 20. In a system of broadcast distribution, a central station and subscribers stations with wired circuits extending between them, means at the central station for producing modulated high frequency wave trains suitable for transmission over the subscribers lines, and a common radiator also at the central station for propagating said modulated wave trains in the subscribers lines by radiation thereto.

521. In a system .of broadcast distribution, a subscribefls station having a telephone line and a telephone set, together with a high frequency receiving set connected to said telephone line, having a telephone transmitter and circuit connected the same as the telephone set, but with a step down transformer connected to the output terminals of the high frequency receiver. and a low resistance telephone receiver connected on the low side of said transformer. said telephone receiver being connected with its transmitter so as to be useful as an extension telephone set over the telephone line and also as a loud speaker or receiver for the radio set.

2:]. In a system of broadcast distribution, a central otlice and subscribers stations with wired lines interconnecting them, means at the central station for distributing high frequency modulated wave trams to the subscribers over their line circuits, a telephone set at a subscriber-"s station, adapted for telephonic use only over his line circuit. and a combined telephone and high frequency receiving set connected in parallel to the line, and provided with means whereby the same telephone receiver may be used to reproduce the modulations received through the high frequency receiver. and to reproduce Speech received over the telephone lines direct.

23. In a system of broadcast distribution. a central station, a plurality of subscribers stations and wired line circuits interconnecting them. together with a telephone at each subscribcfis station, means at the central station for interconnecting the lines for telephonic conversation thcreover, and a combined telephone talking set and high frequency receiver, connected as an extension telephone across the telephone line at a sub scribers station. together with means at the central station to distribute modulated high frequency wave trains over such subs riberslines as are provided with such extension re ceiving instruments.

In a system of radio broadcast distribution. a central. station and plurality of subscribers stations, with line circuits interconnecting them, high frequency receiving means at the subscribers stations, and duplicate heterodyning receiving at the central station. each tuned to receive from a distant station, on a wave length different from the others, but adjusted to deliver to the subscribers currents having a standard wave length.

25. In a system of radio broadcast distribution, a central station, a plurality of subscribers stations interconnecting them, high frequency-receiving means at the subscribers stations, and heterodyning receiving sets at the central station tuned in pairs and connected so that when one apparatus is relaying to the subscribers from a distant station, the second one is ready to replace it, with its oscillating circuit tuned to correspond to the station which it may replace. 26. In a system of radio broadcast distribution, a central station and a plurali}y' of subscribers stations connected therewith by tuned circuits provided with superaudio receiving apparatus tuned to a common stand; ard frequency, a heterodyne receiving instrument at the central station, with a filter coupler and amplifying means for an intermediate or long beat wave carrier, means to receive modulated short waves, at any frequency, whether from distant stations or local oscillators, ahd means to distribute said long wave carrier to'said tuned subscribers lines.

In testimony. whereof I hereunto afiix my signature.

EDWARD E. CLEMENT. 

